In a method of fabricating semiconductor devices, wire bonding in which an electrode of a semiconductor device and a line of a substrate are electrically connected via a wire has been widely used, for example. Typical examples of wire bonding include a so-called ball bonding method. Specifically, a voltage is applied to produce discharge between an electrode and a wire inserted through a bonding tool (e.g., capillary) to form a ball at a tip of the wire. Then, the bonding tool is moved downward toward an electrode of a semiconductor device, and the ball of the wire is bonded onto the electrode of the semiconductor device after applying a load and ultrasonic vibration to the ball.
As a wire-bonding apparatus employing the ball bonding method, there is known an apparatus in which a discharge condition is controlled in order to form uniform balls at as tip of a wire by comparing a value equivalent to Joule heat during ball formation based on a discharge voltage and a discharge current generated between an electrode and a tip of a wire with a set value of a heat amount that has been previously set (cf. PTL 1, for example).